Heat content of the oceans

from Wikipedia, the free encyclopedia
Change in the heat content of the oceans since 1940 at a depth of up to 2000 m
Development of the total heat budget of the earth
  • Warming of the water column 0–700 m
  • Warming of the water column 700–2000 m
  • Warming of the ice and land surfaces as well as the atmosphere

    • As ocean heat content ( engl. Ocean heat content (OHC) ) is the deviation of the sea of the same or even parts (z. B. oceans ) stored thermal energy (the amount of heat ) given to a reference value. Water has a higher heat capacity than air and the total mass of the atmosphere corresponds to a layer of sea water almost 10 m thick, while the oceans are on average 3680 m deep; therefore the heat content of the oceans is higher than that of the atmosphere. The atmosphere has only about 2% of the total heat capacity of the earth .

    The earth is currently warming, primarily as a result of rising greenhouse gas concentrations. The vast majority of the additional energy is stored in the oceans; their increasing heat content is an essential indicator of global warming . The Fifth Assessment Report of the IPCC states that it is very likely that the oceans stored around 93% of the additional energy between 1971 and 2010. More recent estimates published between 2013 and 2018 suggest that ocean warming has accelerated since 1991 and is more pronounced than indicated in the 2013 IPCC report. Because of the thermal expansion of water, the warming of the oceans is a significant contributor to sea ​​level rise .

    The research of ocean heat is the subject of oceanography and climatology .

    definition

    The area-related heat content of a water layer extending from h1 to h2 can be exceeded if the temperature field is known

    and has the unit J / m 2 .

    There are - water density, - specific heat capacity of sea water, h2 - lower depth, h1 - upper depth, - field of potential temperatures of the water.

    determination

    When determining the heat content of the oceans, a distinction is often made, for historical reasons, between the first 700 m of the water surface and the water masses below, the deep sea . The water temperature is measured using various methods, often with a nansen bottle .

    To determine the temperature of the deep sea in particular, the Argo program has existed since 2000 , in which, as of 2020, 3000 floating buoys ( floats ), which dive up to 2000 meters deep at regular intervals, determine and display temperature, conductivity and pressure a satellite system. The data obtained are intended mainly for climatologists interesting that the anthropogenic climate change research. Evaluations of the data from the ARGO project show that surface winds distribute the surface warm water vertically.

    Changes

    OHC values ​​fluctuate from year to year due to climate variability, e.g. El Niño events , or due to errors in measuring instruments.

    Model studies have shown that during the La Niña years, changing winds increasingly transport warmer water masses into deeper ocean layers via ocean currents . This leads to higher heat absorption in the deep sea and less in the atmosphere and near-surface water layers. Decades of increasing heat content at depths below 750 m have been associated with negative phases of the inter-decadal Pacific Oscillation (IPO) . During the El Niño years of the ENSO circulation, ocean currents carry significantly fewer water masses into the deep sea, which means that the temperatures of the water and the atmosphere rise more sharply near the ocean surface .

    The anthropogenic global warming is reflected in the increase in temperatures and the heat content of all water layers. Water layers close to the surface heat up much faster than deep ones. A group led by the Chinese atmospheric physicist Lijing Cheng stated in a paper published in 2020 the increase in OHC in the period 1960–2019 with a total of 370 ± 81 zettajoules (ZJ). Of this, 41% were at depths of 0–300 m, 21.5% at 300–700 m, 28.6% at 300–700 m and 8.9% at less than 2000 m. While the heat content increased at a rate of around 2.1 ZJ per year from 1955 to 1986, it was around 9.4 ZJ from 1987 to 2019. The oceanic heat content increases most clearly in the Atlantic Ocean and in the Southern Ocean , the latter absorbing around 40% of the additional heat energy between 1970 and 2017 at depths of 0 to 2000 m. The increase in OHC was accompanied by increasing heat transport across the equator. Marine heat waves that threaten ecosystems and fisheries often occur in regions of the sea that are particularly warm.

    Energy generation

    The heat content of the oceans has been researched as a renewable form of energy since 1881. This form of energy generation has so far proven to be impractical. With the exception of a few test facilities, no such power plant was put into operation.

    literature

    • JP Abraham et al. a .: A review of global ocean temperature observations: Implications for ocean heat content estimates and climate change . In: Reviews of Geophysics . August 2013, doi : 10.1002 / rog.20022 (open access).

    Individual evidence

    1. ↑ Global Ocean Heat Content estimate from 1940 to 2018 (v3), L. Cheng, January 2019. See also: Lijing Cheng, Kevin E. Trenberth, John Fasullo, Tim Boyer, John Abraham, Jiang Zhu1: Improved estimates of ocean heat content from 1960 to 2015 . In: Science Advances . March 2017, doi : 10.1126 / sciadv.1601545 .
    2. ↑ S. Levitus, JI Antonov, TP Boyer, OK Baranova, HE Garcia, RA Locarnini, AV Mishonov, JR Reagan, D. Seidov, ES Yarosh, MM Zweng: World ocean heat content and sea level change thermosteric (0-2000 m ), 1955-2010 . In: Geophysical Research Letters . 39, No. 10, 2012. doi : 10.1029 / 2012GL051106 .
    3. ^ A b Stefan Rahmstorf : What ocean heating reveals about global warming ( English ) September 25, 2013. Accessed September 29, 2013.
    4. ↑ Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers . In: IPCC Fifth Assessment Report . September 2013, pp. 1–36.
    5. ↑ Lijing Cheng, John Abraham, Zeke Hausfather, Kevin E. Trenberth: How fast are the oceans warming? In: Science . January 11, 2019, doi : 10.1126 / science.aav7619 .
    6. ^ Henk A. Dijkstra: Dynamical oceanography , [Corr. 2nd print.]. Edition, Springer Verlag, Berlin 2008, ISBN 978-3-540-76375-8 , p. 276.
    7. ↑ Argo FAQ website . Retrieved January 14, 2020.
    8. ↑ Magdalena A. Balmaseda, Kevin E. Trenberth, Erland Källén: Distinctive climate signals in reanalysis of global ocean heat content . In: Geophysical Research Letters . 40, No. 9, 2013, pp. 1754-1759. doi : 10.1002 / grl.50382 .
    9. ↑ a b Lijing Cheng, John P. Abraham , Jiang Zhu, Kevin Edward Trenberth , John Fasullo, Tim Boyer, Ricardo Locarnini, Bin Zhang, Fujiang Yu, Liying Wan, Xingrong Chen, Xiangzhou Song, Yulong Liu, Michael E. Mann : Record-Setting Ocean Warmth Continued in 2019 . In: Advances in Atmospheric Sciences . February 2020, doi : 10.1007 / s00376-020-9283-7 .
    10. ↑ Gerald A. Meehl, Julie M. Arblaster, John T. Fasullo, Aixue Hu & Kevin E. Trenberth: Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods . In: Nature Climate Change . 1, 2011, pp. 360-364. doi : 10.1038 / nclimate1229 .
    11. ↑ Meehl, Gerald A., Aixue Hu, Julie M. Arblaster, John Fasullo, Kevin E. Trenberth: Externally Forced and Internally Generated Decadal Climate Variability Associated with the Interdecadal Pacific Oscillation . In: Journal of Climate . 26, 2013, pp. 7298-7310. doi : 10.1175 / JCLI-D-12-00548.1 .
    12. ↑ Rob Painting: A Looming Climate Shift: Will Ocean Heat Come Back to Haunt us? ( English ) June 24, 2013. Retrieved September 29, 2013.
    13. ↑ James Chiles: The Other Renewable Energy . In: Invention and Technology . 23, No. 4, 2009, pp. 24-35.